Showing papers on "Surface tension published in 1996"
TL;DR: In this article, a numerical solution of the Navier-Stokes equation using a modified SOLA-VOF method was used to model the impact of water droplets on a flat, solid surface using both experiments and numerical simulation.
Abstract: Impact of water droplets on a flat, solid surface was studied using both experiments and numerical simulation. Liquid–solid contact angle was varied in experiments by adding traces of a surfactant to water. Impacting droplets were photographed and liquid–solid contact diameters and contact angles were measured from photographs. A numerical solution of the Navier–Stokes equation using a modified SOLA‐VOF method was used to modeldroplet deformation. Measured values of dynamic contact angles were used as a boundary condition for the numerical model. Impacting droplets spread on the surface until liquid surface tension and viscosity overcame inertial forces, after which they recoiled off the surface. Adding a surfactant did not affect droplet shape during the initial stages of impact, but did increase maximum spread diameter and reduce recoil height. Comparison of computer generated images of impacting droplets with photographs showed that the numerical model modeled droplet shape evolution correctly. Accurate predictions were obtained for droplet contact diameter during spreading and at equilibrium. The model overpredicted droplet contact diameters during recoil. Assuming that dynamic surface tension of surfactant solutions is constant, equaling that of pure water, gave predicted droplet shapes that best agreed with experimental observations. When the contact angle was assumed constant in the model, equal to the measured equilibrium value, predictions were less accurate. A simple analytical model was developed to predict maximum droplet diameter after impact. Model predictions agreed well with experimental measurements reported in the literature. Capillary effects were shown to be negligible during droplet impact when We≫Re1/2.
1,049 citations
TL;DR: A general introduction to foams, the initial stages in the production of foams in aqueous solution, foam structures and the classification of bulk foams according to their lifetimes and stability are presented in this paper.
601 citations
25 Dec 1996
TL;DR: It is suggested that dissolved gas (microbubble) gradients between macroscopic bubbles plays an important role in the coalescence process of bubble coalescence by electrolytes.
Abstract: The surface tension of aqueous solutions of simple inorganic electrolytes (36 in total) have been measured by the maximum bubble pressure method as a function of electrolyte concentration up to 1 M. In most cases the surface tension increased, however in a minority of cases, certain combinations of cations and anions had a negligible effect or decreased surface tension. Results were analysed in terms of surface tension/electrolyte concentration gradients ( d (Δγ)/ dc ) and this parameter was found to correlate with the entropies of ion hydration, Jones–Dole viscosity coefficients and dissolved oxygen gradients. Calculation of Gibbs surface deficiencies for selected electrolytes were carried out using the raw surface tension data. Discussion of the surface tension/electrolyte concentration gradients was extended to the mechanism of inhibition of bubble coalescence by electrolytes. The Gibbs–Marangoni effect did not provide a satisfactory explanation for the inhibition of coalescence for all electrolytes and from the present study we suggest that dissolved gas (microbubble) gradients between macroscopic bubbles plays an important role in the coalescence process.
523 citations
TL;DR: In this paper, the authors compared molecular dynamics simulations of a bilayer of 128 fully hydrated phospholipid (DPPC) molecules, using different parameters and macroscopic boundary conditions.
Abstract: We compared molecular dynamics simulations of a bilayer of 128 fully hydrated phospholipid (DPPC) molecules, using different parameters and macroscopic boundary conditions. The same system was studied under constant pressure, constant volume, and constant surface tension boundary conditions, with two different sets of charges, the single point charge (SPC) and extended single point charge (SPC/E) water model and two different sets of Lennard‐Jones parameters for the interaction between water and methyl/methylene. Some selected properties of the resulting bilayer systems are compared to each other, previous simulations, and experimental data. It is concluded that in relatively high water concentration it is possible to use ab initio derived charges with constant pressure boundary conditions. The SPC water model gives a larger area per head group and a broader interface than the SPC/E model. Increasing the repulsion between water oxygens and CH2/CH3 groups has a large effect on the width of the interface an...
496 citations
TL;DR: In this article, the authors measured the surface tension and subsumption properties of difunctional organic acids in various concentrations of (NH4)2SO4 and NH4HSO4 aqueous solutions.
Abstract: Solubilities and surface tensions were measured for difunctional organic acids in various concentrations of (NH4)2SO4 and NH4HSO4 aqueous solutions. Model results using these data indicate that the organic compounds affect cloud droplet growth by two mechanisms: by gradual dissolution in the growing droplet which affects the shape of the Kohler growth curve, and by lowering of surface tension which decreases the critical supersaturation.
451 citations
TL;DR: Under conditions of flow, data are presented to show that the dominant viscous mechanism comes from the slip that occurs when the membrane flows over the cytoskeleton, and a linear relation between tether force and tether velocity is predicted.
408 citations
TL;DR: In this article, surface tension measurements of two series of cationic surfactants, each with two hydrophilic and three hydrophobic groups in the molecule (Geminis and Geminis), were used to study micelle formation and premicellar behavior.
Abstract: Micellization and premicellar behavior of the two series of cationic surfactants, each with two hydrophilic and two hydrophobic groups in the molecule (“gemini” surfactants), one series with a rigid, hydrophobic spacer, and second with a flexible, hydrophilic one, have been studied by use of surface tension measurements. The data show the expected regular increase in surface activity with an increase in alkyl chain length for the shorter chain homologs but show increased deviation from the regularity with an increase in chain length when the number of carbon atoms in the alkyl chain exceeds a certain number. This deviation in surface activity appears to be due to the formation of small, non-surface active aggregates. Equilibrium constants calculated for the aggregation reaction show that the conditions facilitating micelle formation also favor formation of these premicelles, such as lower temperature, stronger ionic strength of the solution, and increased alkyl chain length. Geminis with a flexible, hydro...
323 citations
TL;DR: In this article, the authors address the problem of scaling the combined effects of sample shape, boundary conditions, and viscosity ratios with only minor variations in other parameters, such as sample size, shape and boundary conditions.
Abstract: Spontaneous imbibition is of critical importance to oil recovery from fractured reservoirs. A widely used approach to prediction of oil recovery involves scale-up of laboratory results to reservoir conditions. Scaling involves the effects of sample size, shape, boundary conditions, viscosity and viscosity ratios, interfacial tension, pore structure, wettability, capillary pressure and relative permeability. This work addresses the problem of scaling the combined effects of sample shape, boundary conditions, and viscosity ratios with only minor variations in other parameters. Imbibition measurements are presented for cylindrical Berea Sandstone cores of different lengths. For some experiments, core surfaces were partially sealed with epoxy to give different boundary conditions. Cores were initially saturated with refined mineral oils of different viscosities. A synthetic reservoir brine was used as the wetting phase. A characteristic length was defined as the square root of the ratio of volume to the summation of the ratios of area of core surface open to imbibition to the corresponding distance from the surface to the no-flow boundary. The characteristic length, in combination with a term that compensates for the effect of viscosity ratio, gave close correlation of all data.
267 citations
TL;DR: Although surface tension appears to be a critical factor in the stabilization of proteins, its increase by co‐solvent does not ensure increased stabilization, as the binding of ligands can reduce significantly, or even overwhelm, its effects.
Abstract: The stabilization of proteins by a variety of co-solvents can be related to their property of increasing the surface tension of water. It is demonstrated that, during the thermal unfolding of proteins, this increase of the surface tension can be overcome by the increase in the temperature of the solution at the midpoint of the transition, Tm, and the weak binding of co-solvent molecules. Three such co-solvents were studied: trehalose, lysine hydrochloride (LysHCl), and arginine hydrochloride (ArgHCl). Trehalose and LysHCl increase the midpoint of Tm. The increase of the surface tension by addition of trehalose is completely compensated by its decrease due to the increase in Tm. However, for LysHCl, the increase of the surface tension by the co-solvent is partly reduced by its binding to the protein. For trehalose, preferential interaction measurements with RNaseA demonstrate that it is totally excluded from the protein. In contrast, LysHCl gives evidence of binding to RNaseA. ArgHCl also increases the surface tension of water. Nevertheless, Tm of RNaseA decreases on addition of ArgHCl to the solution. Preferential interaction measurements showed very small values of preferential hydration of the native protein, indicating extensive binding of ArgHCl to the protein. During unfolding, the amount of additional ArgHCl binding is sufficiently large to counteract the surface tension effects, and the protein is destabilized. Therefore, although surface tension appears to be a critical factor in the stabilization of proteins, its increase by co-solvent does not ensure increased stabilization. The binding of ligands can reduce significantly, or even overwhelm, its effects.
235 citations
TL;DR: In this paper, the authors discussed the significance of the line tension in three-phase systems and the contribution of the linear free energy to the energy of attachment (detachment) of fine particles at (from) an interface.
224 citations
TL;DR: In this article, a diblock copolymer of deuterated styrene and isoprene was chemically modified to incorporate pendant fluorinated side chains (fingers) by forward recoil spectrometry, and surface segregation and interfacial segregation of the modified block copolymers from a polystyrene matrix were observed in as-spun films.
Abstract: A diblock copolymer of deuterated styrene and isoprene (dPS−PI) with a small volume fraction of isoprene was chemically modified to incorporate pendant fluorinated side chains (“fingers”). The composition distribution of the diblock copolymers within a high molecular weight polystyrene (PS) homopolymer was determined by forward recoil spectrometry. Surface segregation and interfacial segregation of the modified block copolymers from a polystyrene matrix are observed in as-spun films. Equilibrium segregation was achieved on annealing at 160 °C for several days. The segregation isotherms at the air−polymer interface are shown to be quantitatively described by a self-consistent mean field theory (SCMF), and these permit us to estimate an effective Flory parameter which describes the attraction of the fluorinated segments to the surface and their repulsion from the bulk. The change in the surface tension as a result of the adsorption of the block copolymers at the air−homopolymer interface was evaluated from ...
TL;DR: In this paper, the issues of wetting and filling carbon nanotubes are reviewed together with the possibilities of chemical modification of the nanotube surface and it is shown that all wetting results are consistent with the existence of a surface tension cut-off value at c. 100-200 mN/m above which a liquid will no longer wet nanotsubes.
TL;DR: In this paper, the effect of varying initial liquid-solid contact angle on the evaporation of single droplets of water deposited on a stainless steel surface was studied using both experiments and numerical modeling.
TL;DR: In this article, the interfacial tension of 10 normal alkane + water/brine and hydrocarbon mixture + brine systems were measured by using a pendent drop instrument.
Abstract: Interfacial tensions of 10 normal alkane + water/brine and hydrocarbon mixture + water/brine systems were measured by using a pendent drop instrument The temperature and pressure ranges of measurements are (25 to 80) °C and (1 to 300) bar, respectively The effects of temperature, pressure, and salt content have been studied It was found that the interfacial tension is sensitive to temperature and salt concentration but weakly dependent on pressure and salt species
TL;DR: In this paper, an order parameter representation of a two-phase binary fluid is used in which the interfacial region separating the phases naturally occupies a transition zone of small width, and a modified Navier-Stokes equation that incorporates an explicit coupling to the order parameter field governs fluid flow.
Abstract: A mesoscopic or coarse‐grained approach is presented to study thermo‐capillary induced flows. An order parameter representation of a two‐phase binary fluid is used in which the interfacial region separating the phases naturally occupies a transition zone of small width. The order parameter satisfies the Cahn–Hilliard equation with advective transport. A modified Navier–Stokes equation that incorporates an explicit coupling to the order parameter field governs fluid flow. It reduces, in the limit of an infinitely thin interface, to the Navier–Stokes equation within the bulk phases and to two interfacial forces: a normal capillary force proportional to the surface tension and the mean curvature of the surface, and a tangential force proportional to the tangential derivative of the surface tension. The method is illustrated in two cases: thermo‐capillary migration of drops and phase separation via spinodal decomposition, both in an externally imposed temperature gradient.
TL;DR: In this paper, a nonlinear surface equation of state that accounts for surface saturation and nonideal interactions among the surfactant molecules is adopted, and the linear framework results are recovered for Γ′ that are sufficiently dilute.
Abstract: The shape of a drop centered in an axisymmetric extensional flow is determined by the viscous stresses that deform the drop and surface tension γ′ that resists the deformation. The ratio of these stresses is given by the capillary number, Ca. When Ca is small enough, the drop attains a steady shape. However, above a threshold value, Cacr, the drop elongates continuously, and no steady shape is attained. When surfactants are present on the drop interface, the surface tension is determined by the surface concentration profile, which varies throughout the deformation process. Initially, the surface tension is given by γeq′, in equilibrium with the uniform surface concentration Γeq′. When the flow is initiated, surfactant is swept toward the drop tips, reducing the surface tension there, and altering the interfacial stress balance tangentially through Marangoni stresses and normally through the Laplace pressure. In this paper, the effects of an insoluble surfactant on drop deformation are studied. In previous work, either a surface equation of state for the surface tension γ′ that is linear in the surface concentration Γ′ was used, an approximation that is valid only for dilute Γ′, or Γ′ sufficiently dilute for the linear approximation to be valid were studied. In this paper, a nonlinear surface equation of state that accounts for surface saturation and nonideal interactions among the surfactant molecules is adopted. The linear framework results are recovered for Γ′ that are sufficiently dilute. As Γ′ is increased, the effects of saturation and surfactant interactions are probed at constant initial Γeq′ and at constant initial γeq′. Finally, the case of strong intersurfactant cohesion is treated with a first‐order surface phase transformation model. At moderate surface concentrations, these nonlinear phenomena strongly alter the steady drop deformations and Cacr relative to the uniform surface tension and linear equation of state results.
TL;DR: Computer simulations at fixed surface area, which can explicitly determine pressure anisotropy at the molecular level, should ultimately lend insight into the value of gamma 0, including its dependence on lipid composition and other membrane components.
TL;DR: In this article, the surface phenomena which are derived are directional movement and assembly of fine colloid particles in thin liquid films were derived, and two distinct mechanisms were now postulated to explain this novel fabrication, (i) they are assembled by convective water flow, stimulated by evaporation at the boundary of the particle arrays (films), (ii) they were packed by the long-range attractive force acting between particles induced by surface tension at the film surface.
TL;DR: In this article, the authors measured the disjoining pressure and surface tension isotherms for solutions containing mixtures of charged surfactants and an anionic random-block copolymer, acrylamide−acrylamidesulfonate.
Abstract: Foam-film disjoining pressure and surface tension isotherms are measured for solutions containing mixtures of charged surfactants and an anionic random-block copolymer, acrylamide−acrylamidesulfonate. When combined with an anionic surfactant, dioctyl sulfosuccinate (AOT), the polyelectrolyte shows no indication of direct surface interactions and the surfactant behaves as a simple electrolyte. However, when copolymer is added to cationic dodecyltrimethylammonium bromide (C12TAB) solutions, strong polymer−surfactant interactions create an enhanced adsorption of both components to the air−water interface. The resulting polymer−surfactant surface layers subsequently produce long-range thin-film interactions that have not been seen before. For the C12TAB−polymer solutions, film stratification is observed 3 orders of magnitude below the critical micelle concentration and nearly two orders of magnitude below the critical aggregation concentration (cac). This new type of film stratification is consistent with rec...
TL;DR: In this article, a nonlinear diffusion equation for the liquid shape is derived from mass conservation and Poiseuille flow conditions and a similarity transformation for this nonlinear equation is obtained and the resulting ordinary differential equation is solved numerically for appropriate boundary conditions.
Abstract: The problem of capillary-driven flow in a V-shaped surface groove is addressed. A nonlinear diffusion equation for the liquid shape is derived from mass conservation and Poiseuille flow conditions. A similarity transformation for this nonlinear equation is obtained and the resulting ordinary differential equation is solved numerically for appropriate boundary conditions. It is shown that the position of the wetting front is proportional to (Dt)½ where D is a diffusion coefficient proportional to the ratio of the liquid-vapour surface tension to viscosity and the groove depth, and a function of the contact angle and the groove angle. For flow into the groove from a sessile drop source it is shown that the groove angle must be greater than the contact angle. Certain arbitrarily shaped grooves are also addressed.
TL;DR: In this paper, the authors present a theory for the kinetics of surfactant adsorption at the interface between an aqueous solution and another fluid (air, oil) phase.
Abstract: We present a theory for the kinetics of surfactant adsorption at the interface between an aqueous solution and another fluid (air, oil) phase. The model relies on a free-energy formulation. It describes both the diffusive transport of surfactant molecules from the bulk solution to the interface and the kinetics taking place at the interface itself. When applied to nonionic surfactant systems, the theory recovers results of previous models and justifies their assumptions. Common nonionic surfactants are predicted to undergo a diffusion-limited adsorption, in accord with experiments. For salt-free ionic surfactant solutions, electrostatic interactions are shown to drastically affect the kinetics. The adsorption in this case is predicted to be kinetically limited, and the theory accounts for unusual experimental results obtained recently for the dynamic surface tension of such systems. Addition of salt to an ionic surfactant solution leads to screening of the electrostatic interactions and to a diffusion-lim...
TL;DR: In this paper, the authors obtained detailed capillary kinetic data for flow of a series of alcohols with various surface tension to viscosity ratios, spreading in open V-shaped grooves cut in Cu with three different groove angles.
Abstract: We have obtained detailed capillary kinetic data for flow of a series of alcohols with various surface tension to viscosity ratios, {gamma}/{mu}, spreading in open V-shaped grooves cut in Cu with three different groove angles. Two theoretical models which assume Poiseuille flow and static advancing contact angles were tested against the experimental data. One is a detailed hydrodynamic model with the basic driving force resulting from the pressure drop across a curved interface. The second depends on the total interfacial energy change, independent of the shape of the liquid interface. Both agree with the experimental data. Both predict numerical values in general agreement with experiment and with each other. In the threshold region where the transition occurs between filled and empty regions of the groove, the liquid height decreases linearly with distance, within experimental limitations, and forms an angle which roughly scales as the contact angle for a significant fraction of the threshold region. On the basis of the present detailed experimental data for both kinetics and threshold profile, the differences between experiment and theory and between the theoretical models are insufficient to allow a clear choice between the models. 20 refs., 11 figs., 3 tabs.
TL;DR: In this article, a simple ion-binding model is presented to quantify the equilibrium adsorption of ionic surfactants at aqueous-fluid interfaces, and an analytic expression for the surface tension is obtained as a function of physicochemical parameters of the system.
TL;DR: In this paper, a numerical procedure for the solution of vapor bubble growth with radial symmetry from the thermodynamic critical size in an initially uniformly superheated liquid, including the influences of surface tension, liquid inertia and heat diffusion, is presented in the form of time varying interface radius, velocity, acceleration and temperature.
TL;DR: In this article, the Gibbs adsorption equation was used to explain the surface tension of non-surface active anionic polyelectrolyte (poly(acrylamide sulfonate)) mixed with various surfactants.
Abstract: Equilibrium surface tension measurements have been carried out on solutions of a non-surface-active anionic polyelectrolyte (poly(acrylamide sulfonate)) mixed with various surfactants. While the surface tension does not change when the polymer is added to nonionic and anionic surfactant solutions, a strong synergistic lowering of the surface tension is found with cationic surfactants. In the latter case, we also find that the surface tension is practically independent of the amount of polymer over the range of concentrations studied. Assuming that the polymer stretches out at the interface to form a neutral complex with the surfactant, this behavior can be explained by the classical Gibbs adsorption equation. Furthermore, ellipsometry measurements on these solutions are consistent with our adsorption model.
TL;DR: In this paper, the nonlinear dynamics of an axisymmetric liquid bridge held captive between two coaxial, circular, solid disks that are separated at a constant velocity are considered, and the bridge deforms and ultimately breaks when its length attains a limiting value, producing two drops that are supported on the two disks.
Abstract: In this paper, the nonlinear dynamics of an axisymmetric liquid bridge held captive between two coaxial, circular, solid disks that are separated at a constant velocity are considered. As the disks are continuously pulled apart, the bridge deforms and ultimately breaks when its length attains a limiting value, producing two drops that are supported on the two disks. The evolution in time of the bridge shape and the rupture of the interface are investigated theoretically and experimentally to quantitatively probe the influence of physical and geometrical parameters on the dynamics. In the computations, a one-dimensional model that is based on the slender jet approximation is used to simulate the dynamic response of the bridge to the continuous uniaxial stretching. The governing system of nonlinear, time-dependent equations is solved numerically by a method of lines that uses the Galerkin/finite element method for discretization in space and an adaptive, implicit finite difference technique for discretization in time. In order to verify the model and computational results, extensive experiments are performed by using an ultra-high-speed video system to monitor the dynamics of liquid bridges with a time resolution of 1/12 th of a millisecond. The computational and experimental results show that as the importance of the inertial force – most easily changed in experiments by changing the stretching velocity – relative to the surface tension force increases but does not become too large and the importance of the viscous force – most easily changed by changing liquid viscosity – relative to the surface tension force increases, the limiting length that a liquid bridge is able to attain before breaking increases. By contrast, increasing the gravitational force – most readily controlled by varying disk radius or liquid density – relative to the surface tension force reduces the limiting bridge length at breakup. Moreover, the manner in which the bridge volume is partitioned between the pendant and sessile drops that result upon breakup is strongly influenced by the magnitudes of viscous, inertial, and gravitational forces relative to surface tension ones. Attention is also paid here to the dynamics of the liquid thread that connects the two portions of the bridge liquid that are pendant from the top moving rod and sessile on the lower stationary rod because the manner in which the thread evolves in time and breaks has important implications for the closely related problem of drop formation from a capillary. Reassuringly, the computations and the experimental measurements are shown to agree well with one another.
TL;DR: In this paper, two series of cationic surfactants, each with two hydrophilic and two hyrophobic groups in the molecule (gemini) have been synthesized and the dynamic behavior of their aqueous solutions was studied by the maximum bubble pressure method.
TL;DR: In this article, the surface characterization of polystyrene microspheres was performed by x-ray photo-electron spectroscopy and critical surface tension measurements, and the correlation between the surface composition and wett ability properties of the particles surface and their size and size distribution was also demonstrated.
Abstract: Polystyrene microspheres were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Surface characterization of the formed particles was performed by x-ray photoelectron spectroscopy and critical surface tension measurements. The influence of different reaction parameters, i.e., monomer concentration, stabilizer type (polyvinylpyrrolidone, copolymers of vinylpyrrolidone and vinylacetate and polyvinylace tate), stabilizer concentration and molecular weight, and initiator type and concentration, on the molecular weight and on the size and size distribution of the formed polystyrene microspheres was investigated. The correlation between the surface composition and wett ability properties of the particles surface and their size and size distribution was also demonstrated. © 1996 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 34:1857–1871, 1996
TL;DR: In this paper, the relationship between the excess Gibbs energy in the bulk phase and that in the surface phase which are used in Butler's equation for surface tension was derived for molten ionic solutions as well as molten alloys.
Abstract: The authors discuss the application of thermodynamic solution databases, which have been constructed so far to calculate thermodynamic properties and phase diagrams, to the evaluation of surface tensions of molten alloys, salt mixtures and oxide mixtures. In particular, the relationship between the excess Gibbs energy in the bulk phase and that in the surface phase which are used in Butler's equation for surface tension was derived for molten ionic solutions as well as molten alloys. In this work, the surface tensions of some liquid binary alloys, various molten salt mixtures, which mainly consist of alkali cations and halide anions, and some molten oxide mixtures, in particular binary silicate systems, were calculated and compared with experimental values.
TL;DR: In this article, the adsorption of C12E4 molecules onto a fresh air−water interface was investigated by using video-enhanced pendant bubble tensiometry, and it was concluded that the adaption process is of diffusion control and the diffusion coefficient is 6.4 × 10-6 cm2/s.
Abstract: The adsorption of C12E4 onto a fresh air−water interface was investigated by using video-enhanced pendant bubble tensiometry. From the comparison between the equilibrium surface tension data and the theoretical relaxation profiles predicted by the Frumkin adsorption isotherm, the adsorption process was found to be anticooperative. Dynamic surface tension data for C12E4 molecules absorbing onto a freshly created air−water interface for different bulk concentrations were used for the determination of the controlling mechanism and the evaluation of diffusivity. Comparison was made for the entire relaxation period of the surface tension data and the model predictions. It is concluded that the adsorption process is of diffusion control and the diffusion coefficient is 6.4 × 10-6 cm2/s. The lower limit of the adsorption rate constant of C12E4 were obtained from the theoretical simulation. Besides, the pendant bubble, at which the interface had reached the equilibrium state, was expanded rapidly and a relationsh...